Planting machines are in very wide use in many sections of agriculture. Some are adapted to plant seeds, and others have mechanism capable of handling seedling plants. Various forms of these machines have found applications in the production of almost all forms of farm produce, and in reforestation projects. The planting of seeds is normally handled by an automatic feeding mechanism supplied by a hopper, and seedling plants are usually hand-fed into a mechanical system that deposits the plants properly in spaced relationship. These machines either have arrangements for opening a furrow ahead of the planting mechanism, and closing it afterward, or are equipped to stab an opening in the ground in which the seed or seedling is deposited. Machines constructed along these lines are described in U.S. Pat. Nos. 3,125,044; 3,728,805; and 4,290,373. These patents are all owned by the assignee of the present application.
A problem that is always present in the design of these machines is the incorporation of sufficient flexibility of spacing of the planting operations to accommodate a wide variety of plant requirements. Spacing is normally controlled by the rate of operation of the planting mechanism with respect to the forward speed of the vehicle to which the machine is attached. Another problem has arisen in the planting of seedlings. Deposit of these small and delicate plants along uneven ground will frequently distort the final position of the plants, and impair their ability to survive. Even where furrows are opened and closed by the machine, the presence of clods of small hills adjacent to the furrows can easily distort the plants placement as the furrow is closed. Another undesireable variation in the position and spacing of the plants arises from the ground slippage of the usual rimmed wheels that close the furrows behind the planting position, and are also used to drive the mechanism. The peripheral configuration of these wheels is predetermined by their furrow-closing functions, which is somewhat impractical for the generation of traction. The present invention is directed at the solution of these problems.